The present invention relates to a method for correcting defects in a photomask or reticule. Photomasks of the related art are typically formed using opaque metal films such as Cr or an attenuated phase shifting mask material such as MoSiON deposited by sputtering onto a glass substrate such as silicon glass so that the mask pattern brings about a transformation due to differences in the transmittance of light. Therefore, when performing monitoring/repair using a defect repairing apparatus employing an ion beam as a charged particle beam, electrons are irradiated to perform charge neutralization in order to prevent primary ions from being curved due to charge-up of the mask and in order to prevent it from becoming possible to no longer observe secondary ion images or secondary electron images. When design rules are not severe, image used for confirmation of defective regions that are sufficient for practical purposes can be obtained by optimizing the charge neutralization conditions. However, as a result of recent severity of design rules, with isolation patterns or patterns (OPC patterns) introduced to correct optical proximity effects of exposure apparatus, it has become difficult to observe shapes correctly at the ends of patterns, and charge neutralization conditions have become different for every pattern. In addition, the presence of small features has meant that viewing has become impossible even if charge neutralization is performed using electrons. Necessary repair to satisfy the specifications sought in defect repair cannot be achieved because correct confirmation of defects cannot be achieved for these kind of detailed isolation patterns or OPC patterns.
In addition to having a high spatial resolution, an atomic force microscope is also capable of observing insulators with a high resolution. First, a region of a mask including a defect is observed with the atomic force microscope (AFM) and a pattern including the shape and position of the defect is extracted from an AFM image. The extracted pattern is then converted to a shape format usable by a repairing apparatus using an ion beam and saved. Then a pattern that is observable with the repairing apparatus employing an ion beam is selected as a position alignment pattern. The mask in which the defect is recognized using the AFM is then moved to the apparatus employing an ion beam. A pattern including the defect extracted and converted from the AFM image is then read in. A position alignment pattern for an extracted pattern is then combined with a pattern corresponding to a secondary electron image for the repairing apparatus employing an ion beam and extraction is performed by the AFM. A defect region finely adjusted using alignment of the position alignment pattern is then corrected using an ion beam.
Operation
An AFM capable of high resolution observation even for insulating materials is used to recognize defects and a pattern that is not subject to the influence of charging up is lined up for position alignment. High precision repairing of defects which it was, up until now, difficult to correct using defect repairing apparatus employing ion beams is now possible. Further, if the extent of irradiation with an ion beam is controlled by actively utilizing height information obtained during AFM observation, a problem of detecting end points using ion signals for which images could not be seen due to charging up is resolved, and high quality repairing of defects is possible even for black defects.